In a cellular network comprising a plurality of base stations, each base station has one or more associated cells. A mobile station in communication with a serving cell may to need to handover to a new target cell to maintain connectivity. In a handover procedure, such as when a user terminal moves from the coverage area of one cell to that of another, a new connection to the target cell is set up and the connection to the old cell may be released.
When handover is required, the mobile station measures the signal quality of a number of neighboring cells and this is used in selecting a suitable target cell. This measurement phase is referred to as scanning. To reduce the scanning time and battery consumption, the mobile station scans only neighboring cells included in a list that is defined and broadcast by the serving cell. This list is called neighbor cell list (NCL). A mobile station is handover-covered if there is at least one neighboring cell of the NCL that provides it with sufficiently good signal quality for it to handover to that neighboring cell if necessary. To enhance handover performance, and also to minimize the impact of scanning, the NCL must contain only sufficient neighboring cells such that any mobile needing to perform a handover from its serving cell is handover-covered.
Currently, in a UMTS network for example, the NCLs for the base stations are set up manually, for example, using field measurements, with the help of centralized offline planning tools. Allocation of scrambling codes is also manually implemented using planning tools. If the network is modified, for example if new base stations are deployed, it requires the procedures to be repeated.
US patent application US 2007/0213086 describes a method for automatically configuring an NCL for a base station. To initialize the NCL, the base station sends a cell information list (CIL) to a mobile station and requests measurement reports for those cells included in the list. The base station uses the reported measurements to determine which of the base stations included in the CIL should be included in the NCL for that base station. Subsequently, the NCL may be automatically updated by requesting new measurement reports from a mobile terminal and using the reports to modify the NCL if appropriate.